The invention relates to a brushless, electronically-commutated motor, of the type having a permanent-magnetic outer rotor, in which a stator is disposed, with the stator having three windings or winding stands that are offset by 120xc2x0 electric from one another, with 0.5 coils being wound per pole and strand, and with each winding strand comprising a plurality of winding coils, whose coil width is smaller than the rotor pole pitch, and which are inserted into winding grooves of the stator.
Electronically-controlled electric motors are gaining prominence in numerous fields of application. These motors are electric motors in which the necessary, periodic switching of coils is no longer performed by a commutator, but by electronic switching devices. The electronic switching devices may include, for example, suitable sensors that determine when the stator and the rotor for the coils to be switched are located in a relative position that facilitates or necessitates switching. Of course, the electronic switching devices must also ensure that current is supplied to the respective coil(s) in the appropriate flow direction.
Electronically-controlled electric motors are already known. In such motors, permanent magnets are used either for the stator poles or the rotor poles. Permanent magnets offer several advantages, such as the absence of current consumption, small dimensions, and simple manufacture and assembly. Electric motors of this type are currently used in many technical fields, e.g., as drive motors for air conditioners or servo devices in motor vehicles. The allotted space for an electrically-operated ventilator for cooling the cooler is notably limited in internal combustion engines that are installed longitudinally with respect to the travel direction of the motor vehicle. Conventional permanent-magnet motors cannot be used because of their large overall axial length.
DE 35 42 542 A1 discloses a disk-memory drive having a drive motor without a commutator, which includes a stator that is provided with a winding, and an outer rotor that has permanent-magnet motor magnets and extends coaxially around the stator, forming an air gap. Because the winding coils are connected in series in each winding strand, a higher current flows through the winding coils. This in turn stipulates a current displacement, which leads to a reduced efficiency. Moreover, this state of the technology includes only two pole pairs, so the higher cogging torques also create more noise.
DE-AS 1 613 005 discloses a DC motor that has no commutator, and has a permanent-magnet rotor with single- or four-pole pairs and a plurality of stationary windings or strands, which can be connected consecutively to a constant DC source by way of a control circuit. The motor shaft is advantageously embodied directly as capstan shaft of a tape recorder; this capstan shaft can be switched to different rpms to attain different tape speeds. The winding coils of this motor are not located in the stator grooves, and are therefore not subjected to a current displacement.
German Published, Non-Examined Patent Application DE 36 38 228 A1 discloses a leg sheet stack for a dynamoelectric machine, and particularly a method for producing a salient-pole motor having an electronically-commuted commutator motor for driving a washing machine. This application discloses a circuit board that is connected to the ends of concentrated windings. These windings are electronically commuted in at least one pre-selected sequence in order to excite the electric motor. In particular, the used circuit board has conductor paths for connecting the individual coils.
It is the object of the invention to improve a brushless, electronically-commutated motor such that it has an axially flat structure, is simple to produce, is lightweight and has a high level of efficiency. This object generally is accomplished by a brushless, electronically-commutated motor, particularly as a drive motor for a motor-vehicle fan drive, having a permanent-magnetic outer rotor, in which a stator is disposed, the stator having three winding strands that are offset by 120xc2x0 electric from one another, with one half of a coil being wound per pole and strand, and with each winding strand comprising a plurality of winding coils, whose coil width is smaller than the pole pitch, and which are inserted into winding grooves of the stator; and wherein: each winding strand comprises a plurality of parallel-connected winding coils, the outer rotor has at least p=3 pole pairs; and a circuit board having current conducting bars is provided for connecting the individual winding coils.
Because of its short-pitched windings, the EC motor of the invention has the advantage that the winding heads cannot overlap, which notably effects a small overall axial length.
Because the coils of a winding strand are connected in parallel, the conductor cross section of a winding decreases until a plurality of parallel-connected positions is not necessary inside a winding groove. Each winding therefore has a plurality of parallel current branches. An advantage of the parallel connecting of the coils is the reduction of a current displacement in the winding grooves, as is known from a synchronous rotors. This improves the motor efficiency.
According to a preferred advantageous embodiment of the subject of the invention, the circuit board has four current bars, with one current bar respectively being associated with each of the three winding strands for connecting the beginnings of the parallel-connected winding coils, and the fourth current bar serving to connect the star point to the ends of all of the winding coils of the three winding strands. This feature facilitates the automation of the EC motor production.
Further advantageous embodiments and modifications of the subject of the invention are disclosed.